This is a little long, but it should clear things up for some people.
The average DAT scores for applicants and matriculants have definitely gone up over the years. However, the average DAT score for all test-takers have remained somewhere between 17 and 18 since the late 90s.
In 2000, the average DAT score for all test-takers was 17.6. In 2010, it was 17.6 and even today ADA says "18 typically signifies average performance." I couldn't find the data, but it's probably somewhere between 17 and 18.
In 2000, the average DAT score for the applicants was 17.8. In 2010, it was 18.2 and now it is around 19.
In 2000, the average DAT score for the matriculants was 17.8. In 2010, it was 19.3 and now it is around 20.
Does this mean that the improved test prep materials have made the DAT easier, so that anybody can get a 22+ easily? Hardly.
It is no coincidence that the average DAT score hovers between 17 and 18. The ADA, using various methods for test standardizing, makes sure it stays there. As the DAT prep materials get better and people start doing better, the ADA adjusts the DAT and makes it harder, with the aim of keeping the average somewhere between 17 and 18. If they kept the questions at the same level all the time, the test prep industry would catch on and everybody would get a 21+. That would render the DAT useless as a tool for differentiating the applicants.
The standardizing is done by constantly updating the tests based on the latest data (e.g. some of the questions you answered are unscored and are used for test construction). Of course, it is not perfect, hence the deviation in percentiles for two equal scores (they used to tell you percentiles for each section, and it was slightly different for every test even when the scores were equal).
You may have noticed that the 2009 DAT was slightly more difficult than the 2007 DAT. That's the ADA working to keep up with the test takers.
Granted, there are always outliers but overall, 17-18 will be the average score no matter how great test prep materials get, as long as ADA keeps up the good work.
Thus, the conclusion we should come to based on the increase in the applicant/matriculant scores is not that the DAT has become easier to beat, but that the surge in the number of DAT takers has resulted in more people with higher scores, which in turn increased the number of applicants with higher scores. Of course, this raised the standard since there is less reason to choose someone with <18 when there are 7000 people (60% of the applicant pool) getting 19+ with only about 6000 seats to go around. Moreover, people with lower scores are less likely to apply, further driving up the average score of the applicant pool.
Oh, and I think people can still be proud of their 19-20. That's roughly 70-80th percentile, and despite what SDNers tell you, it still gives you a decent shot at getting in. In 2016, 40.9% of the matriculants had 19-20 while 41.1% had 21+.
